An electric four wheel drive (e-4WD) system can achieve both of a 4WD function and a hybrid electric vehicle (HEV) function by driving the rear wheels of a front-engine in a front-wheel drive vehicle.
Vehicles equipped with an electric four wheel drive system have an engine and a transmission connected to the front wheels. The electric four wheel drive vehicles have a power generator which charges a high-voltage battery using the mechanical energy from the engine.
A motor and a reduction gear, that are driven by electrical energy, are connected to the rear wheels, and the output from the motor and the reduction gear can be transmitted to the rear wheels.
In a regenerative braking mode, braking and inertia energy can be recovered by the motor, and the high-voltage battery can be charged by the recovered energy.
As a type of the electric four wheel drive system, there is a dual clutch type equipped with a dual clutch selectively preventing power transmitted to the rear wheels from the driving elements of the reduction gear and the motor.
An electric four wheel drive system of the dual clutch type includes power transmission mechanisms at both sides of a drive shaft of a hollow motor and multi-plate clutches selectively connecting driving elements with the rear wheels.
The electric four wheel drive system of the dual clutch type can selectively connect the driving elements with the rear wheels by means of the multi-plate clutches and can achieve torque vectoring that actively distributes driving torque to the rear wheels.
The electric four wheel drive system of the dual clutch type is equipped with hydraulic pressure generators that operate the multi-plate clutches, respectively, in order to achieve torque vectoring. The hydraulic pressure generator includes a hydraulic pump disposed in a housing and generating hydraulic pressure, a hydraulic motor providing a driving force to the hydraulic pump, and hydraulic valves and hydraulic lines for supplying the hydraulic pressure to the clutches, respectively.
The electric four wheel drive system of the dual clutch type can control the hydraulic pressure generator in accordance with a torque vectoring duty calculated on the basis of conditions such as understeer and oversteer.
According to the related art, the electric four wheel drive system of an dual clutch type can distribute the torque of the driving elements to one of the rear wheels by controlling the multi-plate clutches by means of the hydraulic pressure generator in accordance with traveling conditions of the vehicle.
However, since the electric four wheel drive system of the dual clutch type includes the pump housing, the hydraulic pump, the motor, the valve housing, and the hydraulic valves, which are components of the hydraulic pressure generator for driving the multi-plate clutches, it is disadvantageous in terms of the entire weight, cost, size, fuel efficiency. In addition, the structure is complicated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and, therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.